Automobile spark ignition and diesel engines have valve train systems, including valves, cams and rocker arms which present special lubrication concerns. It is extremely important that the lubricant, i.e. the engine oil, protects these parts from wear. Further, it is important for engine oils to suppress the production of deposits in the engines. Such deposits are produced from non-combustibles and incomplete combustibles of hydrocarbon fuels (e.g., gasoline, diesel fuel oil) and by the deterioration of the engine oil employed.
Engine oils use a mineral oil or a synthetic oil as a base oil. However, simple base oils alone do not provide the necessary properties to provide the necessary wear protection, deposit control, etc. required to protect internal combustion engines. Thus, base oils are formulated with various additives, for imparting auxiliary functions, such as ashless dispersants, metallic detergents (i.e., metal-containing detergents), antiwear agents, antioxidants (i.e., oxidation inhibitors), viscosity index improvers and the like to give a compounded oil (i.e., a lubricating oil composition).
A number of such engine oil additives are known and employed in practice. Zinc dithiophosphates, for example, are contained in most all of the commercially available internal composition engine oils, especially those used for automobiles because of their favorable characteristics as an antiwear agent and performance as an oxidation inhibitor.
U.S. Pat. No. 4,201,684 discloses using lubricating oils containing sulfurized fatty acid amides, sulfurized fatty acid esters, or ester-amides of alkoxylated amines, such as diethanolamine. Other additives in the oils include zinc dithiophosphate, metal or sulfurized phenates, and metal hydrocarbyl sulfonates.
U.S. Pat. No. 4,394,276 discloses using lubricating oils containing sulfur-containing alkane diols as friction reducing agents. In one embodiment, the oils also contain a metal hydrocarbyl sulfonate, a metal phenate, a zinc dithiophosphate, and a borated alkenyl succinimide or succinate or mixtures thereof.
U.S. Pat. No. 4,394,277 discloses using lubricating oils containing borated sulfur-containing 1,2-alkane diols as friction reducing agents. In one embodiment, the oils also contain a metal hydrocarbyl sulfonate, a metal phenate, a zinc dithiophosphate, and a borated alkenyl succinimide or succinate or mixtures thereof.
U.S. Pat. No. 4,505,829 discloses using lubricating oils containing a polycarboxylic acid-glycol ester, an oil-soluble alkenyl succinimide or borated alkenyl succinate, and either a metal hydrocarbyl sulfonate, a metal phenate, a sulfurized phenate, or a zinc dithiophosphate.
U.S. Pat. Nos. 4,563,293 and 4,629,576 disclose using lubricating oils containing borated long-chain 1,2-alkane diols as friction reducing agents. The oils also contain a metal hydrocarbyl sulfonate, a metal phenate, a zinc dithiophosphate, and a borated alkenyl succinimide or succinate or mixtures thereof.
U.S. Pat. No. 3,933,659 discloses lubricating oil composition which comprise a major amount of an oil of lubricating viscosity, and an effective amount of each of the following: (1) an alkenyl succinimide, (2) a Group II metal salt of a dihydrocarbyl dithiophosphoric acid, (3) a compound selected from the group consisting of (a) fatty acid esters of dihydric and other polyhydric alcohols, and oil soluble oxyalkylated derivatives thereof, (b) fatty acid amides of low molecular weight amino acids, (c) N-fatty alkyl-N,N diethanol amines, (d) N-fatty alkyl-N,N-di(ethoxyethanol) amines, (e) N-fatty alkyl-N,N-dipoly(ethoxy) ethanol amines, and (f) mixtures thereof, and (4) a basic sulfurized alkaline earth metal alkyl phenate. Such lubricating compositions are useful as functional fluids in systems requiring fluid coupling, hydraulic fluid and/or lubrication of relatively moving parts, particularly as automatic transmission fluids.
U.S. Pat. No. 4,032,461 discloses using a lubricating oil composition having a boron derivative of alkyenylsuccinic acid imide, zinc dithiophosphate, calcium alkylbenzene-sulfonate, and sulfurized oxymetal dithiocarbamate.
U.S. Pat. No. 4,960,528 discloses using in an engine crankcase a formulated motor oil containing a small amount of the combination of (i) an overbased alkaline earth metal sulfonate, (ii) a zinc dihydrocarbyl dithiophosphate, (iii) a sulfurized carboxylic acid ester, and (iv) a sulfurized fatty acid amide, ester or ester-amide of an oxyalkylated amine or mixtures thereof.
The use of dithiocarbamates in lubricating oils is well known in the art.
U.S. Pat. No. 3,876,550 discloses lubricating compositions containing an alkylene bis(dithiocarbamate), as an antioxidant, and a substituted succinic acid as a rust inhibitor. The alkylene dithiocarbamate is represented in the patent by the formula R.sup.1 R.sup.2 N--C(S)--S-alkylene-S--C(S)--NR.sup.3 R.sup.4. Example 5 of the patent describes a crankcase lubricant containing a viscosity improver, an ashless dispersant and methylene bis(dibutyldithiocarbamate). The patent further teaches that the composition may also contain various other additives, for example, detergents, dispersants, viscosity improvers, extreme pressure agents, antiwear additives, etc., as well as other oxidation inhibitors and corrosion inhibitors and cites an extensive list of extreme pressure agents, corrosion inhibitors and antioxidants, including zinc salts of phosphorodithoic acid.
U.S. Pat. No. 4,529,526 discloses the use of a sulfurized oxymetal dithiocarbamate with a boron derivative of alkyenylsuccinic acid imide, zinc dithiophosphate, and calcium alkylbenzene-sulfonate.
The use of methylene bis(dibutyldithiocarbamate) as an oxidation inhibitor in lubricating oils, in combination with other ingredients, is also disclosed in U.S. Pat. Nos. 4,125,479 and 4,880,551.
U.S. Pat. No. 4,879,054 is directed to cold temperature greases and teaches using dithiocarbamates such as Vanlube 7723, i.e., 4,4'-methylene bis(dithiocarbamate), in such greases to provide extreme pressure antiwear properties. Examples 13-18 describe using Vanlube 7723 and triarylphosphate as replacements for lead naphthenate and zinc dithiophosphate.
The use of dithiocarbamates as extreme pressure antiwear additives is also taught by U.S. Pat. No. 4,859,352, and U.S. Pat. No. 4,648,985 teaches that the combination of dithiocarbamates with zinc dithiophosphate and copper salts of carboxylic acid provide lubricants with extreme pressure properties.
U.S. Pat. No. 4,383,931 discloses using lubricating oils containing an oil-soluble molybdenyl bis-.beta.-diketonate in combination with zinc dithiophosphate. Methylene bis(dihydrocarbyldithiocarbamates) are used as ashless antioxidants and extreme pressure agents.
U.S. Pat. No. 4,501,678 discloses using lubricating oils containing an alkyl thiocarbamoyl compound and either a molybdenum thiocarbamoyl compound or a molybdenum organophosphorodithioate.
U.S. Pat. No. 4,609,480 discloses using lubricating oils containing an alkyl thiocarbamoyl compound and a 1,3,4-thiadiazole compound. The oils can also contain, among other things, sulfurized oxymolydenum organophosphorodithioates.
A problem has arisen with respect to the use of zinc dithiophosphate, because phosphorous derivatives poison catalyst components of catalytic converters. This is a major concern, because effective catalytic converters are needed to reduce pollution and to meet governmental regulation designed to reduce toxic gases, such as hydrocarbons, carbon monoxide, and nitrogen oxides, in internal combustion engine exhaust emission. Such catalytic converters generally use a combination of catalytic metals, such as platinum or variations, and metal oxides and are installed in the exhaust streams, e.g., the exhaust pipes of automobiles, to convert the toxic gases to nontoxic gases. As before mentioned these catalyst components are poisoned by the phosphorous component, or the phosphorous decomposition products of the zinc dithiophosphate; and accordingly, the use of engine oils containing phosphorous additives may substantially reduce the life and effectiveness of catalytic converters. Therefore, it would be desirable to reduce the phosphorous content in the engine oils so as to maintain the activity and extend the life of the catalytic converter.
There is also governmental and automotive industry pressure towards reducing phosphorous content; for example, United States Military Standards MIL-L-46152E and the ILSAC Standards defined by the Japanese and United States Automobile Industry Association require engine oils to have phosphorous content below 0.12 wt. %. The phosphorous content in most high grade engine oils containing zinc dithiophosphate is approximately 0.1 wt. %, and thus meet the 0.12 wt. % requirement. Nevertheless, it would be desirable to decrease the amount of zinc dithiophosphate in lubricating oils still further, thus reducing catalyst deactivation and hence increasing the life and effectiveness of catalytic converters. However, simply decreasing the amount of zinc dithiophosphate presents problems because this necessarily lowers the antiwear properties and oxidation inhibition properties of the lubricating oil.
Meanwhile, recent engines installed in motor cars are apt to be used to satisfy severe demands (high speed and/or high power) and the viscosity of engine oils tends to be more and more lowered to reduce viscous resistance in order to improve fuel-efficiency. For these reasons, conditions concerning lubrication of engines are becoming severer and severer, and therefore the antiwear property of engine oils is becoming more and more important. However, the known engine oils, which contain detergent-dispersant and zinc dithiophosphate as main additive components, can not satisfactorily prevent engine troubles caused by wear. Therefore, it is desired to take measures to meet this problem.